This one is so simple and it works like a charm. What are some other quick tricks for mimicking accents?

I'm a fan of your 'generative' approach to accents, in that the details flow naturally from general starting principles. Instead of focusing on each word, you focus on the physicality of the speech apparatus, and the right sounds emerge.

Hm! I think that the Indian tongue position is the easiest "trick" because it doesn't require you to not do anything that you're accustomed to.. it just sticks a big obstacle in your way and makes you work around it.

Some of the most obvious "big changes" I can immediately bring to mind include

German: closed throat, tongue on back of teeth
British: only front muscles, nasal air flow
Texan: only back muscles (except where absolutely necessary, and even then the action is in the back)
California surfer: back of throat hanging open low

...but these don't really require you to do something that actively interferes with how you speak, as the Indian tongue position. They require you to passively interfere with your own speech patterns.. in a way, to introduce mental blocks instead of physical.